The stub post replaces the main page - not the individual post pages, not archive retrievals, label searches, etc.

The stub post contains a minimum of information.

The stub post is simply better than nothing.

But now, maybe you can provide something a bit better than a simple stub post, to let your readers know that your blog now has a new URL.
Part of the recently offered Search preferences features include a pair of redirection options. This won't eliminate the anti-spam policy - you still can't redirect outside the base blog URL - but you can, maybe, improve redirection inside the base blog URL.

Custom Page Not Found.

Custom Redirects.

Custom Page Not Found

If you think about it, a stub post is really just a fancy "Page Not Found" post, hosted on the main page. If all pages within the blog simply redirect immediately to a "Page Not Found" display - and if you can make the display look like it's designed as part of the blog, then you have a better stub post.

You can make the stub post more relevant to your readers.

You can make the stub post immediately visible - for individual post pages, archive retrievals, label searches, etc - as well as for main page access.

And, a better stub post makes a better stub blog.

Custom Redirects

If you're still not satisfied with the single stub post approach, you can redirect specific URLs, within the blog, to other URLs within the blog. If you have identified individual posts, specific label searches, etc that get lots of visitor traffic, you can redirect those page URLs to pages or posts that provide more specific information than the custom (but still generic) "Not Found" stub post.

Both the Custom Page Not Found and Custom Redirects options are part of "Errors and redirections" in Settings - "Search preferences", in the New Blogger GUI.

You can't redirect any old blog URLs to the new blog URL - even with the new Search preferences features - but you can make it easier for your viewers to understand that your blog has moved - and maybe link directly, from individualised stub posts, to specific URLs within the new blog. And, you can do any of this, any time it's convenient.

Setup the original, main page view based stub post, immediately.

Setup a Custom "Page Not Found" stub post, later.

Setup individual Custom Redirects, as you identify any high traffic single post activity.